Control system for automatically fed furnaces for solid organic fuels



Oct. 27, 1953 w. J. HATTON 2,656,799 CONTROL SYSTEM FOR AUTOMATICALLYFED FURNACES FOR SOLID ORGANIC FUELS Filed Sept. 9, 1949 3 Sheets-Sheetl INVENTOR WILLARD J; HATTON Oct. 27, 1953 w J HATTON I 2,656,799

CONTROL SYSTEM FOR AUTOMATICALLY FED FURNACES FOR SOLID ORGANIC FUELSFiled Sept. 9, 1949 3 Sheds-Sheet INVENTOR WILLARD HATTON Oct. 27, 1953w. J. HATTON. 2,656,799

CONTROL SYSTEM FOR AUTOMATICALLY FED FURNACES FOR SOLID ORGANIC FUELSFiled Sept. 9, 1949 r 3 Sheets-Sheet 3 j INVENTOR;

8g WILLARD J. HAT'TON;

Patented Oct. 27, 1953 FED FURNACES FOR FUELS soLn) ORGANIC Willard J.Hatton, Jackson, Mich., assignor, by

mesne assignments, to Bituminous Coal Research, Inc., Washington, D.C-.-,-a corporation of Delaware Application September 9,1949,-;SerialNo. 114,771 r This invention relates to a control systemfor automatically regulating the depth of a live fuel bed in anautomatically fed furnace for solid organic fuels. More particularly, itrelates to a differential pressure control to achieve such regulation ina stoker-fed coal furnace for residences and small buildings.

This invention is of especial value when used in. connection with thedownflow stoker-fed furnace system for bituminous coals which is morefully disclosed in United States patent application Serial No. 93,562,filed May 16, 1949, in the name of Willard J. I-Iatton and. Ralph A.Sherman, and. assigned to Bituminous Coal Research, Inc By means. of thefurnace system of said application Serial No. 93,562, the substantiallyfully automatic heating'of average size residences and small buildingswith bituminous coals and the like was made feasible using conventionalcontrol circuits.

In the said furnace system, a small furnace is provided to whichbituminous coal and air in correlative amounts are periodically orcontinuously fed as demand requires to the top of a live fuel bed, theupper part of whichis confined andremains in a restricted zone withinthe furnace. A zone of discontinuity is provided substantially at theplane of ignition so that the coal remains relatively cool until it isactually subjected to kindling conditions at the time it is so fed.Under the high rate of burning (relative to the rates of burning inconventional furnaces) that ensures at least during the on periods ofheat demand and hold-fire, all volatile and tarry matter released passesthrough the fuel bed whence the heat release potentiality thereof isrecovered and smoke emission which might otherwise be caused thereby isprevented. The agglomerating properties of such volatile and tarrymatter are suppressed or destroyed during such active burning andremaining agglomerating tendency, if any, is nullified by ignitionsuppression obtained by predetermining the setting of the controlcircuit. The particles in the fuel bed gravitate downwardly into theunconfined lower portion of the combustion chamber where gaseouscombustion products escape through the upper surface of said bed aroundthe restricted zone. Ash also gravitate's downwardly through the fuelbed and out of the combustion chamber before any material clinkeringthereof can take place.

The aforesaid system makes it possible to burn strongly agglomeratingcoals in equilibrium which may be defined as that condition in-which 2Claims. (C1 111 01? the'fuel bed,for a constant rate of primary air,maintains the same character of combustion and thickness. In otherwords, the rate of burning and the rate of ignition remain substantiallyequal and free burning results with the plane of ignition staying in therestricted zone during heat demand and hold-fire periods. The restrictedzone is the upper confined portion of the combustion chamber which opensunrestrictedly into the lower unrestricated portion of the combustionchamber. The fuel bed, which is substantially entirely a live fuel bed,extends up,- wardly into and fills at. least the lowermost end of therestricted zone. It is inherent in furnace systems employing ,avariationof the underfeed principle that some thinning of the fuel bed occurswhen the air rate is increased. Such, a change will shift the plane ,ofignition to some extent within the restricted zonewhich is generally notsufficient, however, to disturb the beds equilibrium.

However, there are, variation factors which would materially tend tochange the level of the plane of ignition ,in a given furnace if suchtendency were not, counteracted. Important factors of this characterarise from the differing agglomeration properties of bituminous coalsfrom different beds, from the different reactivities of the respectivesizes of coal fed to the furnace system, and from fluctuations in heatdemand. On the subject of. size, bituminous coal supplied for, domesticstokers, for example, may vary be tween the approximate size limits fromabout 1 rn aximum to A;" minimum, a wide size consist in terms ofthecombustion reactivity of the size gradations in that consist. Since thefurnace in the system disclosed in application Serial No. 93,562 isrelatively small, any tendency towards it's'b'e'coming upset bydisturbing its equilibrium must be counteracted that much more quickly.Any tendency 'to lose equilibrium is particularly present duringholdfire operation, as distinguished from heat deman'doperation.

In providing the furnace system of application Serial'No.'93,562 with afrusto-conical section in the restricted zone as more fully disclosed inUnited Statespatentapplication Serial No; 98,484 filed June 11, 1949,-inthe name of Willard J. Hatton and Henning M. Carlson, and assigned tdBituminous Coal Research,- Inc., inherent counteraction toany material"change in' the depth of the fuel bed is obtained; Under thislast-mentioned invention any tendency for the fuel bed to deepen'in turntends to'reduce the approximate cross sectional area of the plane ofignition and thus increase the rate of burning; conversely, in the eventof any tendency in the bed to thin, this last-mentioned invention tendsto decrease the rate of burning to again counteract a change in thedepth of the bed.

The present invention provides another novel control for the depth ofthe fuel bed which has particular application in combination with eitheror both of the disclosures in the aforesaid applications. Thus, in thisinvention it has been found that in the event of the deepening of thefuel bed, such as may be brought about by a tendency to initialagglomeration of bituminous coals particularly when in the plasticstage, that there is an increase in the resistance to the flow of gasesthrough the bed which is substantially in proportion to such change indepth. Heretofore, in conventional Stoker-fed furnaces, any

change in the depth of the fuel bed has not been accompanied by anyreliably proportionate change in such resistance. As a consequence, inconventional furnaces, flow resistance is not generally an appropriatebasis for a control of the character disclosed by this invention.

The importance of the discovery in this invention is evidenced by theimportance of maintaining equilibrium burning and hence, fuel beds ofsubstantially constant depth, particularly with agglomerating fuels.bed, even if it does not upset the furnace system or spill out of thefurnace, still results in poorer combustion due to lowered temperatures,decreased surface for contactwith combustion air and decreasedcombustion air supply resulting from increased resistance to the flow ofgases through the bed. In the operation of conventional stokersemploying the un'derfeed principle, there is also a possibility of lossof ignition especially during hold-fire operation if there are largecoke trees in the bed when the air fan is turned on at the beginning ofan on period.

By means of this invention, the possibility of the furnace systembecoming upset or causing other difiiculty with agglomerating coals ismaterially reduced. Moreover, this invention provides assurance againstthe presence of fresh, raw fuel remaining in relatively inactive contactwith a live fuel bed. In such cases, especially during off periods ofthe temperature demand thermostat control system the possibility ofdetrimental smoke emission is increased. Other objects and advantages ofthis invention will be apparent from the following description and from'the drawings, which are illustrative only, in which Figure l is avertical cross sectional view of a residential downfiow stoker-fedfurnace suitable for use in combination with the system of thisinvention;

Figure 2 is a plan view of the entire furnace shown in cross section inFigure 1;

Figure 3 is a schematic view of a preferred embodiment of the controlsystem of this invention applied to a furnace such as is shown inFigures 1 and 2;

Figure 4 is a vertical cross sectional view of the differential pressuredevice illustrated in the control system shown in Figure 3;

Figure 5 is a vertical cross sectional view of the clutch assembly usedin the control system illustrated in Figure 3; and

Figure 6 is a vertical cross sectional view of a modified differentialpressure device which may Otherwise, a deepening fined by surface 25.

layer 24.

5% be used in a modified control system constructed in accordance withthis invention.

Referring to Figures 1 and 2 of the drawings, a furnace l is illustratedwhich has a casing l0 forming the outer wall of a jacket or boiler Hla.Jacket Ifla contains a heat absorbing fluid such as water and has aninner wall consisting principally of a lower tubular inner wall sectionII, an offset intermediate inner wall section l2 and an upper inner wallsection 13. A plurality of vertical flue pipes M are concentricallypositioned around inner wall sections l2 and I3, and extend from offsetwall portion Hi to an annular flue collar thus connecting the latter tothe lower portion of a combustion chamber 29. Flue pipes I4 are sealedaround their respective edges to keep boiler Illa fluid tight.

A cover plate 11 rests on the top of easing l0 and closes flue collar [5to which respective portions of the furnace it is bolted or otherwiseafiixed. A central opening I8 is provided in cover plate H which openingis in registry with the opening at the top of tubular wall section I3. Aturret head [9 closes opening it and has a port therein for theadmission of combustion air. A further port 2| in head [9 is connectedto the delivery end of a conveyor conduit 22 within which a feed screw22a operates to feed bituminous coal or other fuel in predeterminedamounts dependent upon the heat demand and control conditions operativeat the time being. A cover 23 tightly closes a corresponding opening inthe top of head [9. This cover may be removed to insert and ignitekindling at the commencement 'of operations if automatic ignitionapparatus should not be provided.

Wall section I2 is lined with a. refractory material 24 so disposed thatthe innermost surface 25 thereof is substantially in the form of afrustoconical part substantially 'formingan upper restricted portion ofcombustion chamber 29. This refractory 24 thereby increases in lateralthickness in an upward direction and generally inversely to thereduction in internal horizontal cross sectional area'of thefrusto-conical part de- Uppermost inner wall section [3 may be linedwith a sub'stantially'vertical layer of refractory 26 which, at itslowermost edge, meets the uppermost edge of refractory The interiorspace within refractory lining 26 may be regarded as the very top ofcombustion chamber 29 although the plane of ignition is adapted toremain within surface 25 which confines the upper part of the live fuelbed.

The upper portion of combustion chamber 29 opens unrestrictedly into itslower portion, substantially forming the top of an inverted T. Thislower portion broadens out around a conical grate 3|. Grate 3! issupported in fixed, eccentric position on a rotating base 30. Ash passesbetween base 30 and the lower section of jacket I011, into an ash pit 36where it is removed. The lower section of jacket Ilia behind wallsection II absorbs heat directly from the lower portion of the fuel bed,therebyaiding in the maintenance of temperatures at least in the lowerportion of the fuel bed which discourages any material forma- !tion ofclinker by the melting or fusion of ash. Additional cooling in the lowerportion of cornbustion chamber 29 may be obtained if desired by theprovision of some supplemental combustion air through a line 40 and ashpit 36. Such supplemental combustion air will also mix up and burncombustible which might otherwise tend to be present in the ash and inthe gaseous com- 1 shown) remains on.

bustion products. Normally, such Supplemental combustion air would notbe in excess of onequarter by weight of the downflow primary combustionair supp-lied to the furnace through port 29.

A metal liner 2'! surrounds the lower portion of combustion chamber 2%in contact with lower wall section ii. The inside of liner 21' is invertical registry with wall il above it so that fly ash may havesubstantially no non-vertical surface or land on which to deposit in thefurnace. A series of vertical grooves 29 are disposed around the insideof liner 2? and cooperate with a plurality of grooves 3t in grate 3iandwithitslower vertical edge 32 to break up such small clinkerparticles as may form. Sufficient clearance is left between the edge ofbase plate 65 andthe interior of liner 2'! so that only readilyremovable ash falls into ash pit 36. A sweep 31 is adjustably affixed tothe underside of base and pushes ash out of ash pit 36 through anopening 39 leading into an ash removal duct 39. A bottom plate 35 closesthe bottom of ash pit 36 and cas ing 49. Suitable lagging may beprovided for all exposed portions of the furnace.

Base 35 is rigidly mounted on a hollow rotatable shaft 44 havingpassages therein (not shown) through which cooling water may becirculated if, under the particular circumstances of a given furnace,the temperature in the lower portion of the fuel bed tends to be toohigh. A hub block 4! is supported by closure 35 and supports a live fuelbed extending from the upper surface of plate 39 to the plane ofignition within refractory surface 25. a fixed bracket 43 to assist inthe journaling of shaft 44 which is keyed at its upper end to base plate36 and at its lower end to a Worm wheel 45. A worm gear 46 is driveneither continuously or stepwise by appropriate control and drivingmechanism (not shown) during the operation of the furnace system.Heat-absorbing fluid is supplied to jacket Ilia through a pipe 4'! andafter circulation therethrough passes out through an outlet pipe 28.Gaseous combustion products including entrained material after passingthrough the fuel bed filling the lower end of the upper portion ofcombustion chamber 29 make an abrupt turn and pass laterally and thenupwardly through the bed and into the proximate vertical flue pipes i4.Thence, they pass into flue chamber l5 and out through a duct 49 to astack. The vertical surfaces of flue pipe [4 and the absence ofhorizontal ledges around the walls of combustion chamber 29 minimize anypossibility of deposition of fly ash or soot.

Referring to Figure 3, furnace l is supplied with solid organic fuelsuch as an agglomerating bituminous coal through a conveyor or conduitor pipe 50, the upper end of which is connected to the outer end of pipe22. A feed screw 22a having universally coupled sections turns in pipes56 and 22 to feed the coal. A shaft 5| is connected to the lower end offeed screw 22a by a universal joint 52. A clutch assembly 53 ispositioned at the outer end of shaft 51 and is adapted to be disengagedunder proper conditions to stop the coal feed even though theconventional temperature demand thermostat control system (not By suchdisengagement, coal feed screw 22a stops, even though an electricdriving motor 54 continues to run and 0perate a combustion air blower 55during the continuance of such on period. A belt 56 connects motor 54 toclutch assembly 53.

A bushing 42 is provided at the end of K Clutch 'assembly'53 is in' acontrol circuit 5'! which is part of the control system of thisinvention. A schematic wiring diagram for such acircuit 51 isillustrated in Figure 3 but many other Wiring arrangements are possibleand within the skill of the electrical art. A differential pressuremanometer 59 of the bell type is connected in circuit 51 and operates onthe gaseous pressure differential across the fuel bed in furnace l whichis substantially proportional to any change in the depth of the fuelbed. I

In clutch assembly 53 a driven pulley 59 is turned by belt 56. Pulley 59rotates freely about shaft 5| being mounted in an idling bearing 60.A'clutch ring 6| is fastened to pulley 59 about theaxis of shaft 5|.Ring 6| has a conical driving clutch face 62 which cooperates with aclutch face'63 on an axially slidable driven clutch disc 64;A hub 65forming'a part of disc 64 is telescoped over the end of a stud shaft 66which is fastened in the end of shaft 51. A spline 61in a splineway inshaft 66 cooperates with a corresponding longitudinal recess in hub 65to permit axial but not rotatable movement of disc 64 relative to shaft66.

A thrust bearing '68 connects disc 64 with a solenoid link 69,preferably of a non-magnetic metal, so that disc 64 may rotate freelyrelative to link 69 but may not move endwise relative thereto. A pin 19pivotally connects link 69 to a clevis TI which is fastened to theend ofa normally off-center (relative to the winding of a solenoid l4) ferroussolenoid core 12. Core I2 is provided with a threadably and rigidlyengaged non ferrous extension 72a, of a non-magnetic metal like brass,integral with clevis H. Solenoid 14 includes a conventional winding 15and yoke 76 for the longitudinal actuation of core 72 when winding isenergized. A tension spring H is fastened at one 'end through an eyebolt 13 in core "and at the other end about a pin18 spanning the loopedend of a stop 19. Stop 19 is immovably fastened relative to motor 54 andother fixed parts of the equipment and normally engages an enlarged end86 of core 12 under the pull of spring 11. When clutch assemmy 53 is inthe position shown in Figure 5, so long as electric motor 54 turns, feedscrew 22a operates to feed coal into furnace I. However, when solenoid14 is energized, core i2 is displaced to the left and surfaces 63 and62respectively are disengaged, stopping shaft 5| and feed screw 22a.

Manometer 58 comprises a liquid and gas tight casing 8| having asuitable manometer liquid 82 therein. A bell 83 is inverted over the endof a high-pressure pressure tube 84. A low-pressure pressure tube 85 isconnected to the manometer at the top thereof. A vertically adjustablepressure plate 86 is fastened to the inside of casing 8| adjacent thetop thereof for engagement by a pressurepin 81. Pressure pin 81 is apart of a normally closed microswitch 88 pivotally supported at 89inside the manometer to casing 8|. An arm 99 rigidly attached to switch88 is pivoted at 9| to a floating link 92. One end of floating link 92is hingedly connected to a bracket 93 attached to the interior of casing81. The other end oflink 92 i fastened to the top of bell83. Insulatedliquidproof leads '94 are connected to the terminals of switch 86 whichmay be of any suitable conventional nature, and pass out throughsuitable seals 95 in casing 8 I.

.Higherpressure pressure tube 84 extends into the upper portion ofcombustion chamber 29 preferably adjacent the plane of ignition so thatthe static pressure of the incoming combustion air from port 263 will becommunicated through pressure tube 34 to manometer 58. Lower pressurepressure tube 85, on the other hand, is connected on the other side ofthe fuel bed so as to communicate the static pressure of the combustiongases leaving the fuel bed. The location and Conventional character ofthe furnace connections to register these static pressures adjacent theadmission and outlet surfaces of the bed are matters within the skill ofpneumatic engineering and are schematically shown in one possiblelocation for each in Figure 1. Hence, manometer 58 may be set for amaximum predetermined depth of the fuel bed by the vertical adjustmentof pressure plate 85.

As a consequence, after the requisite adjustment is made, upon anypotentially troublesome deepening of the fuel bed the differentialpressure within manometer 58 on the two sidessof bell 83 will increase.Such an increase will cause bell 8,3 to rise within casing 8|, movingpin '8] into contact with pressure plate 86 and opening switch 88.Switch 88 will remain open only so long as such pressure differentialexceeds the predetermined maximum amount corresponding to thepredetermined maximum depth of fuel bed desired.

When switch .88 is broken, control circuit 51 causes solenoid M to beenergized moving ferrous core 12 to the left from the position shown inFigure ,5, thereby disengaging clutch disc 64 from clutch ring BI andstopping shaft 5I. Thereby,,no additional fresh, raw, relatively :coolcoal is fed to furnace I where it would become heated and aggravate thebed-deepening tendency. Of course, when the temperature demandthermostat control system is off, motor 54 will stop and no coal will befed to furnace jI irrespective of the connections within control circuit51.

In circuit 51!, a push-button switch 96 is normally closed and remainsclosed until manually opened to disconnect the control system of thisinvention from the furnace system with which it is employed. Analternating current power source is provided across lines 91 and 98.Line 98 continues through switch 88, a'line 99, a relay coil I69, switch95 and return to line 9]. An armature Iti cooperates with a switch pointI02, the circuit through which is connected by a spring I83 wheneverrelay coil I is deenergized as by the opening of switch 88. Switch.point I02 is connected by line Hill to power line 98. A line Hi5extends from armature II'H through solenoid winding I5, aline IE6, afuse I01 and a line I08 to line 91 on the other side of switch 96.

In operation, therefore, when the pressure differential across the fuelbed in furnace I increases beyond the predetermined maximum signalling aproportionate increase in bed depth, nanometer 58 opens switch 88,thereby closing the circuit in lines I04 and I05 through switch It iI02. This in turn energizes solenoid I4 and stops the coal feed.Conversely, during normal operations with the fuel bed remainingrelatively constant in depth with equilibrium burning, solenoid i4 isnot energized and hence spring 11 maintains driving engagement betweenshaft 5| and motor 54 through clutch assembly 53. Further, since anyparticles of clinker which may tend to be formed are broken up andcrushed between grooves 34, edge 32, the outer periphery of plate 3% andthe cast or milled vertical grooves 28 in liner 2?, no materialdistortion of the accuracy of the differential pressure control systemof this invention can result because of any presence of such particlesin the fuel bed.

In the preferred embodiment illustrated in Figure 3, the control systemof this invention is effective in the event of deepening of the fuel bedin furnace I beyond the prescribed limit. In some types of operation, itmay be desirable to have positive control by a control system embodyingthe principles of this invention, operative also in the event of anundue decrease in the depth of the fuel bed. In such event, as shown inFigure 6, a differential pressure manometer IIIl may be provided.

Manometer III? has a liquid and gas tight casing II l which ishorizontally partitioned by a diaphragm I I2 forming a lower chamber H3and an upper chamber I14. A higher pressure pressure tube {I5 isconnected to chamber IIS and a lower pressure pressure tube .I I6 isconnected to chamber H4. A post H7 is fastened. to di phragm I I2 andpasses through a flexible sealing member II8 whence it terminates in adouble electrical switch contact respectively numbered H9 and I20. Anadjust-able electric switch contact I2! is adapted to cooperate withcontact I I9 and an adjustable electric switch contact I25 is adapted tocooperate with an electrical contact I22. Appropriate leads respectivelynumbered I 26a, I2 Ia and I221; and an appropriate electrical circuit(not shown) maybe provided in a circuit controlling a conventionalmagnetic clutch and in turn respectively controlled by the verticalmovements of rod. Ill. Thus, in the event of excessive deepening of thefuel bed, diaphragm H2 would bow upwardly, closing switch I I9i2 l andstopping the fuel feed by disengagement of such a clutch. On the otherhand, if the fuel bed should tend to thin beyond another predeterminedsetting corresponding to a predetermined minimum. pressure differentialacross the fuel bed as determined by the adjustment of switch contactI20, diaphragm H2 would move to the other side of its electrically opencircuit position, closing switch Mil-422, engaging such clutch andfeeding coal to a furnace such as furnace I. With the use of the controlsystem of this invention. employing such a double-acting differentialpressure control device as manometer I It, the feeding of coal to thefurnace system may if desired be made independent of the on periods ofthe overall heat demand and hold-fire thermostat control systememployed, by having an independent drive motor for the coal feed.

Either of the modifications of the control system of this inventiondisclosed herein, may have the clutch assembly thereof so positionedrelative to the power source that when ever the coal feed is stopped thecombustion air blower and any grate rotating mechanism and ash dischargemechanism may also be stopped. In. the further embodiment shown in theaforesaid application Serial No. 93,562, this result would be obtainedby placing any such clutch assembly between the coal feed driving motorand the transmission gear box. 0n the other hand, by interposing suchclutch assembly between the gear box and coal feed screw, only the coalfeed itself would be affected.

AlthOugh I have illustrated and described a preferred and a modifiedcontrol system in this invention for, the maintenance of a substantiallyconstant depth of fuel bed, it is to be understood that Various es inthe circuits and in the a ement and character of parts may b made withinthe spirit of the invention and the scope of the appended claims.

I claim:

1. In a control system for a residential stokerfed furnace forbituminous coal or the like, apparatus comprising in combination, acombustion chamber in said furnace adapted to contain a fuel bed, saidcombustion chamber having an upper restricted frusto-conical portion anda lower unrestricted portion, said fuel bed being adapted to extendupwardly into said frustoconical portion and be confined thereby, astoker for feeding such coal generally downwardly into saidfrusto-conical portion, driving means for said stoker, a blower forsupplying combustion air generally downwardly into said frusto-conicalportion, means responsive to the static pressure of said combustion airadjacent its area of entrance into said fuel bed, means responsive tothe pressure of the gaseous combustion products emanating from said fuelbed adjacent the area of said emanation, means responsive to thedifferential pressure registered between said bothmentioned pressureresponsive means and adapted to control said driving means, whereby whensaid differential pressure exceeds a predetermined amount, said drivingmeans is disconnected fromv said stoker at least for the period duringwhich such differential pressure exceeds said predetermined amount.

2. In a control system for a residential stokerfed furnace forbituminous coal or the like, apparatus comprising in combination, acombustion chamber in said furnace adapted to contain a fuel bed, saidcombustion chamber having an upper restricted frusto-conical portion anda lower unrestricted portion, said fuel bed being adapted to extendupwardly into said frustoconical portion and be confined thereby, astoker for feeding such coal generally downwardly into saidfrusto-conical portion, driving means for said stoker, a blower forsupplying combustion air generally downwardly into said frusto-conicalportion, means responsive to the static pressure of said combustion airadjacent its inlet into said combustion chamber, means responsive to thepressure of the gaseous combustion products emanating from said fuel bedadjacent the outlet from said combustion chamber, means having two-waymovement responsive to the difierential pressure registered between saidboth-mentioned pressure responsive means and adapted to control saiddriving means, whereby when said differential pressure exceeds apredetermined amount said driving means is disconnected from said stokerat least for the period during which said diiferential pressure exceedssaid predetermined amount, and when said differential pressure fallsbelow a second predetermined amount, said driving means is reconnectedto said stoker.

WILLARD J. HATITON.

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